Posts: 2
From:Newcastle
Registered: Sep 2003

posted September 16, 2003 04:36 PM               

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Twin screw extrusion process for manufacture of pvc continuous sheet - powder mix with addition of recycled pvc pellets is being interrupted by oil seepage at the die head. Oil is tar-like and is not found in the screens, where extrudite is uniform and essentially dry. However 24 inches further forward and a gradual oil seepage across the die lips is resulting in sheet damage on the calendar rolls (sheet is sticking). If extrudite is coming through with full absorbtion of oil, why the oil drop-out at the die head? Die is fishtail type and oil other than that in the mix is introduced at the extruder. Appreciate anyone's help who may have seen this problem.

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Posts: 196
From:Brodheadsville, PA USA
Registered: Jun 2001

posted September 16, 2003 06:49 PM               

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Your die oil is likely the result of using recycled material. Low molecular weight components boil off the extrudate as it exits the die, and condense at the die lips. Recycle often contains more of these low molecular weight components because of thermal degradation. I have learned a few tricks over the years and may be able to help on a consulting basis.

Tom Cunningham
Extrusion Technical Services

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